The invention relates to improvements in methods of and in apparatus for ascertaining one or more characteristics of certain substances, such as tobacco. More particularly, the invention relates to improvements in methods of and in apparatus for ascertaining one or more characteristics (such as the mass per unit length and/or the moisture content) of mass flows of particulate materials, such as fragments of tobacco leaf laminae and/or other smokable substances.
It is already known to ascertain certain characteristics of mass flows of tobacco particles by evaluating the extent of detuning, due to the presence of such substances, of a high-frequency resonator which receives microwaves from a suitable generator and transmits high-frequency signals to a suitable evaluating circuit. The extent of shift of the resonance frequency and damping of such high-frequency signals (in comparison with output signals which are transmitted in the absence of mass flows within the range of the high-frequency resonator) is indicative of the characteristic(s) of the material of the mass flow.
The making of smokers' products, such as plain or filter cigarettes, normally involves a testing of the mass flow of tobacco particles which are to form the rod-like fillers of such products. As a rule, the testing involves a determination of the mass of tobacco per unit length of the mass flow and/or the moisture content of the particles in the mass flow and/or the dielectric constant of tobacco (as used herein, the term "tobacco" is intended to embrace natural, reconstituted and artificial (substitute) tobacco). An accurate determination of the mass per unit length and of the moisture content is particularly important in connection with the making of cigarettes or other rod-shaped smokers' products (hereinafter referred to as cigarettes for short). For example, once the percentages of dry ingredients and moisture in a mass flow of tobacco particles are known, one can accurately determine the overall mass of the tested substance by simple addition of the signals denoting the dry mass and the moisture content. The situation is similar in connection with the processing of certain other substances such as foodstuffs, chemicals, textile materials, paper and many others.
German patent No. 40 04 119 discloses the determination of the moisture content of substances in a cavity resonator which is connected to a microwave generator. The patented apparatus resorts to a calibration curve to ascertain the resonance frequency and the half intensity width of the resonance line.